1. Field of the Invention
The present invention relates to an antenna unit that can be used for a communication terminal or other suitable device and further relates to a communication device including such an antenna unit.
2. Description of the Related Art
FIG. 12 is a schematic perspective view of an antenna 20 provided in a communication device. This antenna 20 has a dielectric substrate 21, a fed radiation electrode 22 and a non-fed radiation electrode 23 that are mounted on the dielectric substrate 21, a feed electrode (not shown) that is located on a predetermined side surface of the dielectric substrate 21 and that feeds the fed radiation electrode 22 a signal, and an antenna-grounding electrode (not shown) disposed on the entire lower surface of the dielectric substrate 21.
The fed radiation electrode 22 has two ends. One of the two ends is a grounding end 22a and the other of the two ends is a feed end that is fed a signal transmitted from the feeding electrode. The non-fed radiation electrode 23 has two ends. One of the two ends is a grounding end 23a and the other of the two ends is an open end.
This antenna 20 is surface-mounted on a ground electrode 26 of a circuit substrate 25 of the communication device. Subsequently, the feed electrode is connected to a signal feeder 27 of the circuit substrate 25. The grounding ends 22a and 23a are directly connected to the ground electrode 26.
In this case, for example, when the signal feeder 27 transmits a signal for communications to the feed electrode of the antenna 20, the feeding electrode transmits the signal to the fed radiation electrode 22. The signal is further transmitted from the fed radiation electrode 22 to the non-fed radiation electrode 23 by electromagnetic coupling therebetween, whereby the fed radiation electrode 22 and the non-fed radiation electrode 23 resonate and perform an antenna operation.
The fed radiation electrode 22 and the non-fed radiation electrode 23 can generate a double-resonance state when various conditions such as the electrical lengths of the fed radiation electrode 22 and the non-fed radiation electrode 23, the distance therebetween, and so forth, are adjusted in an appropriate manner. This double-resonance state increases the characteristic of the antenna 20.
Recently, small and low-profile antennas have been demanded. However, the efficiency of the fed radiation electrode 22 and the non-fed radiation electrode decreases when the dielectric substrate 21 is made smaller and low-profiled. In this case, the characteristic of the antenna 20 is reduced.
In order to overcome the problems described above, preferred embodiments of the present invention provide an antenna unit that is miniaturized and low-profile without reducing the antenna efficiency thereof and a communication device including such an antenna unit.
According to a preferred embodiment of the present invention, an antenna unit for transmitting and receiving a predetermined radio wave includes an antenna body having a dielectric substrate and a fed radiation electrode with a first open end and a first grounding end. The fed radiation electrode is mounted on the dielectric substrate. The antenna body further has a non-fed radiation electrode with a second open end and a second grounding end. The non-fed radiation electrode is provided near the fed radiation electrode and mounted on the dielectric substrate. The antenna unit further includes a substrate for mounting the antenna body thereon. The substrate has a ground electrode thereon, a ground-electrodeless portion extending from at least one portion of an antenna-body mounting area so as to extend off of and away from the antenna-body mounting area, and at least one grounding line disposed on a predetermined area of the ground-electrodeless portion. The predetermined area is outside the antenna-body mounting area. The fed radiation electrode is fed a signal transmitted from a signal feeder. Further, at least one of the first and second grounding ends is connected to the ground electrode via the grounding line.
According to the present preferred embodiment of the present invention, at least one of the grounding ends of the fed radiation electrode and the non-fed radiation electrode is connected to the ground electrode via the grounding line disposed on the predetermined area of the ground-electrodeless portion, the predetermined area being outside the antenna-body mounting area on the ground electrode of the substrate. The grounding line can perform an antenna operation in concert with the fed radiation electrode and the non-fed radiation electrode, which means that an antenna is disposed outside the antenna body. Therefore, it becomes possible to increase the effective size of the antenna body without increasing the actual size thereof and the antenna efficiency.
Further, at least one portion of the antenna-body mounting area functions as a ground-electrodeless portion, which also increases the antenna efficiency. Therefore, preferred embodiments of the present invention can provide a small and low-profile antenna body without decreasing the antenna efficiency.
Further, when the grounding line extends in a predetermined direction crossing the direction along which currents of the fed radiation electrode and the non-fed radiation electrode pass, it becomes easy to independently control a polarized wave in the direction along which the currents pass and a polarized wave in the direction along which the grounding line extends. Therefore, the antenna unit can use a frequency band affected by the polarized wave in the direction along which the currents of the fed radiation electrode and the non-fed radiation electrode pass and a frequency band affected by the polarized wave in the direction along which the grounding line extends, whereby resonance frequencies within the different frequency bands can be adjusted independently. Since the resonance frequencies of the antenna unit can be easily adjusted, it becomes possible to cope with design modifications or other changes without delay.
The first and second grounding ends are disposed on one side surface of the dielectric substrate so as to be adjacent to each other over a predetermined distance, or on different side surfaces of the dielectric substrate, respectively. Further, both the first and second grounding ends are connected to the ground electrode via the grounding lines, respectively, and the grounding lines extend from the first and second grounding ends so as to be spaced away from each other and are connected to the ground electrode. According to the above-described configuration, the intensity of the polarized wave in the direction along which the grounding line extends increases. Therefore, it becomes possible to reduce the interaction of the polarized wave in the direction along which the currents of the fed radiation electrode and the non-fed radiation electrode pass, and the polarized wave in the direction along which the grounding line extends. Subsequently, it becomes easier to adjust the resonance frequencies of the different frequency bands of the antenna unit, respectively.
The ground-electrodeless portion is an area extending from the antenna-body mounting area to an edge portion of the substrate and at least one portion of a side edge of the grounding line is disposed on the edge portion of the substrate. According to the above-described configuration, it becomes possible to use the edge portion which is less suitable for mounting portions thereon and likely to be wasted. Therefore, it becomes possible to produce the antenna unit without reducing most of the effective area of the substrate for forming the elements and the pattern of traces thereon.
The communication device including the antenna unit is miniaturized since the antenna unit is miniaturized and becomes low profile. Further, the reliability of the communication device increases since the antenna efficiency increases.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detail description of preferred embodiments thereof with reference to the attached drawings.